This invention relates to high-temperature machine components. More particularly, this invention relates to methods for manufacture of components for gas turbine engines, and the articles made from the use of these methods.
In a gas turbine engine, compressed air is mixed with fuel in a combustor and ignited, generating a flow of hot combustion gases through one or more turbine stages that extract energy from the gas, producing output power. Each turbine stage includes a stator nozzle (also known as “vane”) having airfoils that direct the combustion gases against a corresponding row of turbine blades (also called “buckets”), each having an airfoil extending from a blade base (also called “platform”), where a joint attaches the blade to a supporting rotor disk, to a blade tip at the opposite end. The turbine airfoils are subject to substantial heat load, and, because the efficiency of a gas turbine engine is proportional to gas temperature, the continuous demand for efficiency improvements translates to a demand for turbine airfoil components (herein referred to collectively as “turbine airfoils) such as nozzles and blades that are capable of withstanding higher temperatures for longer service times.
Turbine airfoils made of single-crystal materials or directionally solidified, columnar-grained materials have been developed to better cope with the rigors of high service temperatures. Although single-crystal components generally exhibit better high-temperature capability relative to directionally solidified components, the processes used to cast single-crystal materials are typically more expensive than directional solidification processes for large components. Moreover, the very high capability of single-crystal material may not be required at all locations of the airfoil component. For example, leading and trailing edges of a turbine blade are often subject to significantly higher temperatures in service than other regions of the blade. Nevertheless, conventional single-crystal casting processes produce components made entirely of single crystal material, even for regions of components that may not require the costly but high-performing material.
Therefore, there remains a need in the art for economical fabrication processes capable of producing turbine airfoil components with structure and properties tailored for stringent service requirements. There is also a need for cost-effective components that meet such requirements.